Inhalers for delivering medicament to a patient by inhalation are known. Such devices include metered-dose inhalers (of both pressurised and dry-powder types). Metered-dose inhalers typically comprise a medicament-containing vessel and an actuator housing having a medicament delivery outlet in the form of a mouthpiece or nosepiece.
The medicament-containing vessel may be a pressurized canister containing a mixture of active medicament and propellant. Such canisters are usually formed from a deep-drawn aluminium cup having a crimped lid which carries a metering valve assembly. The metering valve assembly is provided with a protruding valve stem which, in use, is inserted as a tight push fit into a so-called stem block in the actuator housing.
Metered-dose inhalers may either be of the manually operable type or the breath-actuated type. For the manually operable type, the patient self-administers the medicament by manually pressing the closed end of the canister into the actuator housing to cause movement of the canister relative to its valve stem (which is fixed in the stem block of the actuator housing). This movement is sufficient to actuate the metering valve assembly of the canister, resulting in the pressurised contents of a metering chamber being vented through the stem, through the stem block and its exit jet and orifice, and causing the medicament to exit the mouthpiece or nosepiece as an aerosol mist. Simultaneously with this action, the patient inhales through the nosepiece or mouthpiece, entraining the aerosol mist in the inhaled stream of air. The patient then releases the depression force on the canister which, under the action of an internal valve spring, moves upward with respect to the valve stem, returning to its resting position.
A more recent development is the so-called breath-actuated metered-dose inhaler, which serves to automatically displace the canister relative to its valve stem and release the contents of the canister's metering chamber in response to a patient's inspiration. The general purpose of such inhalers is to alleviate difficulties in coordinating actuation of the metering valve assembly with the patient's inspiration, and to provide for a maximal amount of medication to be drawn into the patient's lungs. A breath-actuated metered-dose inhaler is disclosed in WO 01/93933 A2.
The actuator housing is generally regarded as an integral part of the medicament delivery system, since the design of the housing can greatly affect the form of the medicament generated for inhalation by the patient. The actuator housing of a metered-dose inhaler typically includes an air inlet means for producing an air flow through the actuator housing into which the medicament is released.
Further, for breath-actuated inhalers, the air flow through the actuator housing typically operates or at least influences in some way the breath-actuated mechanism. Consequently, the actuator housing of such inhalers comprises air inlets designed to allow airflow through the housing. However, such air inlets exhibit the problem that they can be covered or occluded by the patient's hand or finger during use, thereby preventing or influencing the airflow through the actuator housing, with the result that the breath-actuated mechanism may malfunction. This problem is often exacerbated by the fact that the air inlets are provided on the actuator housing at positions which are convenient for handling the inhaler during use by the patient.
Thus, there is a need in the art to provide improved airflow configurations for inhalers that are less susceptible to being occluded or blocked by the patient during use, while at the same time allowing for convenient and comfortable operation by the patient.